1. Field of the Invention
This invention is related generally to apparatus for producing a force, and in particular to devices that employ ducted fluids flowing over an airfoil-shaped structure to generate lift, induce motion, or produce power. Still more particularly, it is concerned with methods and means for increasing the efficiency and enhancing the utility of such devices.
2. Description of the Prior Art
The use of shaped ducts for directing the flow of air, water, or other fluids over wing-like structures to generate or enhance lift is well known. A variety of designs embodying combinations of shaped ducts and airfoils have been proposed. Typical examples are illustrated by U.S. Pat. Nos. 2,812,980, 3,276,723, 3,297,228, 3,365,149, 3,489,374, 3,612,445, 3,785,592, 4,117,992, 4,235,397, and 5,170,963. Although promising on paper, few if any of these devices have proven successful in operation, much less commercially useful. Among their many deficiencies, most commonly three, namely, limited performance, low efficiency, and inherent dynamic instability, preclude them from serving a useful purpose.
Heretofore, as exemplified by the cited examples, conventional wisdom called for the use of ducts having axially expanding flow area. By definition, such ducts are diffusers and slow the flow of fluid discharged from them. U.S. Pat. No. 5,155,992, in which I am a co-inventor, discloses an alternative method and means employing a shaped duct and an annular cambered vane for generating a force. The patented invention utilizes a flared body enclosed in a shroud to form a duct terminating in an outlet of axially diminished flow area. A fan or impellor drives a fluid stream through the duct. Having a reduced fluid outlet, the duct defines a nozzle. Precisely opposite from a diffuser, a nozzle serves to accelerate the fluid discharge. The device is designed to direct the discharge over a cambered vane or wing positioned in the duct fluid outlet.
Tests have demonstrated the successful operation of the invention and confirmed its utility. I have discovered that by incorporating certain improvements, features and refinements in the patented device, I can greatly enhance its performance, efficiency and stability. The present disclosure relates to methods employing those improvements, features and refinements, to a force-producing apparatus embodying them, and to mechanisms, such as vehicles, employing.
The subject invention, or some of its features, may be applicable to other prior art devices, but it is intended primarily as an improvement in devices embodying the teachings of U.S. Pat. No. 5,155,992 to generate lift, induce motion, or produce power. Such devices serve a variety of applications. By way of example, they can be used to achieve vertical lift in VTOL/STOL aircraft, or to propel the rotor blades that provide lift for helicopters. Immersed, they can provide propulsion for surface or sub-surface vessels.
For illustrative purposes, several preferred embodiments of the invention will be described in conjunction with a force-generating device in which the vane and shroud embody the generally circular plan form shown in U.S. Pat. No. 5,155,992. In this configuration, the flared body is preferably generally conical, that is, radially symmetrical, in shape, and coaxial with the shroud. The lower end of the flared body extends into and overlaps the flared end of the annular shroud and with the overlapping portion of the shroud forms an annular duct of axially diminishing flow area. The converging walls of the duct define an annular nozzle. The vane, in this design a generally horizontally disposed annular cambered wing, is mounted to the duct in the path of fluid discharged radially outwardly from the nozzle.
In one of the preferred embodiments shown here, the invention comprises a first deflector in the form of an annular skirt mounted to the enlarged upper end of the flared body. This deflector extends outwardly of the flared body into the duct fluid outlet. A second deflector in the form of an annular flange mounted to the lip of the shroud and extending radially inwardly of the shroud (i.e., in the direction of the flared body) into the duct fluid outlet; and a structural feature that I call a xe2x80x9cpressure damxe2x80x9d in the form of a flange depending generally normally from the bottom surface of the vane at or near its trailing edge. At least one of the purposes of the pressure darn is to entrap a portion of the fluid flowing chordwise along the bottom surface of the vane.
In another preferred embodiment of the invention, the shroud of the first embodiment is enclosed in a second shroud that, with the first shroud, forms a second, outer, annular duct (like the first duct a nozzle of upwardly diminishing flow area). The stream of fluid discharged by the annular fluid outlet of this outer duct is directed toward the bottom surface of the vane.
I am not certain as to the precise fluid-dynamic principles called into play by the invention, however, based on my test data, it appears that three functions are in operation: One, served by the first deflector, involves the compression of the fluid discharge and the resulting increase in the velocity of the fluid exiting the duct nozzle. Another, associated with the second deflector, involves the exercise of control over the angle of attack and distribution of the flow of the accelerated fluid mass under and over the cambered vane. The third, influenced if not determined by the pressure dam, has to do with the chordwise location of the region of impact of the fluid discharge against the lower surface of the vane. Individually, these functions offer marginal overall improvement in the operation of the patented device. Collectively, they produce a marked increase in the lift force generated by the device, noticeable improvement in its efficiency, and demonstrably enhanced stability and controllability. The provision of the second shroud appears to increase, and augment the control of, the flow of fluid across the bottom surface of the vane.
It will be understood that the subject invention, though illustrated and described in connection with an annular duct and vane, is readily adaptable for use with a force-generating device of other than annular configuration. By way of example, rather than conical, the flared body may be rectilinear in cross-section with the shroud or shrouds taking the form of curved sheets or surfaces spaced convergently or divergently from its flared wall or walls. FIG. 3 of U.S. Pat. No. 5,155,992 is illustrative of one such non-annular embodiment of the invention. The shape of the vane in such a device would be defined by the configuration of the shroud or shrouds and the flared body. In the non-conical variation of the invention shown in FIG. 3 of U.S. Pat. No. 5,155,992, a pair of straight vanes are positioned in the outlets formed at either side of the bilaterally symmetrical flared body. The pressure dam and first and second deflectors, of course, would conform to the configuration of the vane, the flared body, and the shroud or shrouds, respectively.
A principal object of the subject invention is to provide a method and means for maximizing the force produced by the cambered vane of a device of the type described in my earlier patent.
Another object is to provide a method and means, for use in a device of the type described, for directing the fluid exiting the duct nozzle efficiently under and over the cambered vane.
A further object is to provide a method and means, for use in a device of the type described, in which the velocity of the discharged fluid is increased as well.
Another object is to provide a method and means, for use in a device of the type described, incorporating a pressure dam for increasing the force generated by the fluid impinging on the lower surface of the cambered vane.
Still another object is to provide a method and means, for use in a device of the type described, in which the acceleration and directional control of the fluid are achieved by adjusting the configuration of the duct and its fluid outlet.
A still further object is to provide such a method and means in which the configuration of the duct and fluid outlet are established by a combination of deflectors mounted to the flared body and its surrounding shroud and extending into the duct fluid outlet.
Another object is to provide a method and means, for use in a device of the type described, which incorporates a second annular duct nozzle for increasing the velocity of and directing the discharged fluid impinging on the bottom of the cambered vane.
An additional object is to provide methods and means of the type described for use in force generating devices of other than annular configuration.
Yet a further object is to provide a method and means, for use in a device of the type described, that utilize in combination the configuration of the fluid-containing duct, fluid deflectors associated with a tapered central body and its enclosing shroud, and a pressure dam on the bottom surface of the vane, for maximizing the force generated by, and improving the stability, directional control, and efficiency of, such a device.
Still another object is to provide a method and means, for use in a device of the type described, for generating a force that overcome the deficiencies inherent in the prior art shaped-duct lift-generating devices.